1. Field of the Invention
The present invention relates to a liquid crystal display, mask and method for producing the liquid crystal display. More particularly, the present invention relates to a liquid crystal display having an improved viewing angle characteristic and a method for producing the same.
2. Description of Related Art
In general, contrast and color of a liquid crystal display (LCD) depend on its viewing angle, which is called a viewing angle dependence. One technique to widen a viewing angle of an LCD is to form two types of alignment domains having different alignment properties in an alignment film. For example, as shown in FIG. 9, alignment domains 2 and 3 are formed in a resin film 1 on a lower substrate using this technique. In the alignment domain 2, molecules are oriented in a predetermined direction at a predetermined pretilt angle, and in the alignment domain 3, molecules are oriented in a direction 180-degree different from the molecular orientation in the alignment domain 2 at the predetermined pretilt angle.
An example of the alignment film 4 having the alignment domains 2 and 3 is disclosed in Japanese unexamined Patent Publication No. 05-232441. The Japanese patent publication discloses that alignment domains (A) 2 and (B) 3 are arranged in a checkered pattern on a pixel by pixel basis, as shown in FIG. 10. In accordance with the invention, since a vertical or horizontal line is displayed on a screen of an LCD using the alignment domains (A) 2 and (B) 3 having different alignment properties, the viewing angle of the line can be widened. However, when a thin oblique line having a pixel width is displayed on the screen, it passes through only either the alignment domains (A) 2 or (B) 3, so that the viewing angle dependence cannot be improved.
In order to form the alignment domains (A) 2 and (B) 3 on the resin film 1 in a checkered pattern, a resist pattern is formed on the resin film 1 by a photolithography method, and then ion beams or the like are applied thereto. However, the photolithography method requires a repeat of steps of applying resist, exposing to light, developing, performing an alignment treatment, and removing resist. For this reason, the production of the alignment film 4 is time consuming and costly, and an alignment surface of the film 4 may possibly be damaged in the course of removing resist. Thus, the photolithography method has drawbacks.
In order to solve these problems, it is preferable to use a mask having a predetermined opening pattern rather than a photoresist. Specifically, a mask is put on the resin film 1 to perform an alignment treatment. Through the opening portions of the mask, the molecules of the resin film 1 are partly aligned in a predetermined direction, and the different alignment domain of the film is shielded by the mask. In order to form the aforementioned alignment film 4, there is need to form a checkered mask having apertures for exposing the alignment domains (A) 2 and shielding portions for shielding the alignment domains (B) 3. However, when the aperture ratio of an LCD is high and a pixel pitch is 200 xcexc or so, it is necessary that a joint portion between the rectangular shielding portions of the mask that shield the alignment domains (B) 3 is 10 xcexc or less. However, it is quite difficult to produce such a mask having the size of a liquid crystal panel in high accuracy.
One approach to solve the aforementioned difficulties in producing a checkered mask is, for example, to align alignment domains having the same alignment properties in a row or in a column on a pixel by pixel basis or on a sub-pixel by sub-pixel basis in the case of a color display, as shown in FIG. 11. In this case, a mask having slit apertures for exposing the alignment domains (A) 2 and shielding portions for shielding the alignment domains (B) 3 is formed, for example. However, such a mask having the slit apertures and shielding portions (widths of the shielding portion and the slit aperture: several 10 xcexc length: several 100 mm) over the whole alignment film is low in strength. In addition, when an LCD is used for a computer, a line having only a pixel width may possibly be displayed. In this case, the line is displayed using either the alignment domains (B) 2 or the alignment domains (B) 3, so that a viewing angle characteristic of the line cannot be improved.
An object of the present invention is to provide a liquid crystal display having an improved viewing angle dependence of a displayed image even when any line segment, single-color area, or character is displayed.
Another object of the present invention is to provide a mask suitable for forming a plurality of alignment domains having different alignment properties on an alignment film.
Accordingly, a feature of the present invention is a liquid crystal display that includes an alignment film having first alignment subdomains with a first alignment property and second alignment subdomains with a second alignment property different from the first one. In the alignment film, the first alignment subdomains and the second alignment subdomains are arranged in a matrix so that both of them are included in every line extending across the matrix.
Another feature of the present invention is a mask used for forming an alignment film having first alignment subdomains with a first alignment property and second alignment subdomains with a second alignment property different from the first one. In the alignment film, the first alignment subdomains and the second alignment subdomains are so arranged in a matrix that both of them are included in every line extending across the matrix. The mask of the present invention comprises a plurality of apertures for forming first alignment domains consisting of the first alignment subdomains with the first property, and a shielding portion for shielding a portion where a second alignment domain consisting of the second alignment subdomains with the second property is to be formed. Each of the apertures has a shape corresponding to a predetermined combination of the first alignment subdomains. The shielding portion is physically continuous. The apertures and the shielding portion are so formed that every line extending across the mask passes through at least one of the apertures and the shielding portion.
Still another feature of the present invention includes a method for producing a liquid crystal panel having a pair of substrates facing each other and having aligenment films on their facing surfaces comprises the steps of: preparing a first substrate and a second substrate each having, on one of its surfaces, a base film which is later turned into an alignment film by alignment treatment; preparing a mask having a plurality of apertures for forming first alignment domains consisting of first alignment subdomains with a first property and a shielding portion for shielding a portion where a second alignment domain consisting of second alignment subdomains with a second property is to be formed; subjecting the base film of the first substrate to alignment treatment from a predetermined direction; placing the mask on the surface of the base film of the first substrate; subjecting the base film on the first substrate exposed through the apertures of the mask to alignment treatment from a direction perpendicular to the predetermined direction; subjecting the base film of the second substrate to alignment treatment from the predetermined direction; placing the mask upside down on the base film of the second substrate; and subjecting the base film of the second substrate to alignment treatment from the direction perpendicular to the predetermined direction.
Various other objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views.